In last week's challenge to his readers, Booker introduced them to the concept of the Border Inspection Post (BIP) and the fact that the nearest facility is in Dunkirk (pictured).

With a capacity of 5,000 consignments a year, enlarged from the original 1,000 at a cost of €2 million, it is part of a recently completed upgrade of the ferry port, costing €14.88 million. And yet, the facilities would be woefully inadequate for the post-Brexit traffic from the UK, where there will be customs checks and veterinary inspections on UK goods for the first time since 1992.

The other concept Booker introduced was the inescapable but barely recognised point that the checks and inspection will arise not as a result of the EU specifically imposing controls on the UK, but because the UK has elected to adopt "third country" status with respect to the EU.

To deal with goods from third countries, the EU has developed elaborate systems of control which apply, without discrimination, to all countries in this category. And when the UK leaves the EU and becomes a third country, it will be treated no differently from any other.

These simple concepts, though, seem entirely beyond the capability of some Sunday Telegraph readers to understand – as evidenced from yesterday's letters column.

There, we have – amongst others - Dr Peter R Blower from Great Yeldham, Essex who noted that Booker had raised the problem of BIPs but, "does not mention the equivalent problem that the EU may encounter with its vehicle exports at new UK border inspection posts". Writes Blower: "For every action like this, there could be a reaction. But, as the saying goes, we are not going to hurt one another, are we?"

If this was not such a common reaction, we would be tempted to ignore it (as indeed should have the newspaper). But Dr Blower belongs to that unthinking group which believes that, if the EU took that action, the UK could simply retaliate – in this case by imposing an inspection regime on vehicles from the EU.

In similar vein, we have Chris Platford from Malmesbury in Wiltshire, who seems to think that, if we leave the EEA, "we will be up against new regulations, including border inspection posts". But, he suggests, "it will be in the interest of all EU members that wish to continue exporting to us to make them as uncomplicated as possible".

And then we have Patrick Staunton from London NW1. He seems to think that describing the EU market as "like a fortress against the outside world" is inconsistent with the facts, arguing that restrictions only apply to agricultural produce.

"Changes will have to be made when we leave the EU", writes Staunton. "If, as Mr Booker seems to think, any changes are impossible, then he must be saying that we should continue to be subject to the Common Agricultural Policy. That is hard to believe".

This latter argument is, of course, the classic example of the "straw man" technique. The animal health controls, which require BIP inspection for "third country" imports, exclude all EEA countries from these controls – despite Efta states not being part of the CAP.

And the, if we look to issues such as REACH, medicines approvals, notified bodies and much else, it is plainly obvious that additional controls do not just apply to agricultural produce.

As to the broader issue, the difficulty lies in the complete inability to understand that the rules covering imports from "third countries" are already in place. These people simply don't get the point that there is nothing personal in this. If the UK is an EU Member State, it will be treated as a Member State. If it chooses to become a "third country", it will be treated as a third country.

The idea, therefore, that we should (or could) retaliate in any is simply inappropriate. And the idea of implementing border inspections of vehicles, in retaliation for the EU conducting inspections of animal-based products, is absurd.

Apart from anything else, underlying the entire corpus of trade law is the principle of non-discrimination (relaxed only in certain instances where preferential trade agreements apply). Thus, if we were to impose vehicle inspection on the EU, we would have to adopt a similar regime in respect of all other imports.

As much to the point, though, we are parties to the WTO TBT agreement, in pursuit of which we, as a nation, undertake not to create any new, unnecessary barriers to trade. To implement border inspection of vehicles would very clearly breach that undertaking.

But then to expect the EU to reduce its controls simply because its Member States export to us. The EU, having invested so much political and administrative capital in its system of controls, is not going to dismantle them just because the might inconvenience the UK. The EU is in exactly the same trap – if it gives preferential treatment to us, it is obliged to treat every other "third country" the same. That isn't going to happen.

As to the BIP problem, it is interesting to see that, of the €14.88 million spent on the Dunkirk port upgrade, €12.88 million was invested by Dunkerque-Port and €2 million by the ferry company DFDS. The project only received European Union funding of €1.29 million.

The point here is that additional BIP facilities will require investment by the ports concerned. Governments do not supply the facilities – unless they own the ports. They will require private capital. And, as we have seen, this takes years to plan and implement.

Ironically,. There was in 2015 a redevelopment scheme proposed for part of Dover Port – the Western Docks, which immediately met with a wave of objections. However, the works are to go ahead on the basis that ferry freight traffic through Dover and Calais has increased by 20 percent over the last two years and was expected to rise by a further 40 per cent by 2030.

Ironically, the £200 million scheme is to be part funded by the EU, under the BRIDGE (Building the Resilience of International and Dependent Gateways in Europe) project. In January, it was reported that work was due to start "within weeks", although the effect of Brexit must be uncertain.

Here, it is not only Sunday Telegraph readers who seem to be suffering from a lack of comprehension. Tim Waggott, Chief Executive of the Port of Dover, says that: "Any changes brought forward to the country's trading relationship need to be mindful of the UK's absolute need to maintain the rapid transit of goods and passengers through Dover and our sister ports on the European mainland".

He then goes on to say that the Port remains clear that a barrier-free relationship with the EU - our largest, closest and most important trading partner - must be a critical outcome of the negotiations to ensure we make a success of Brexit".

Yet, that is the very thing Mrs May's policy will ensure that we don't get. Those barriers already exist, and we're set to place ourselves outside them. And that isn't so difficult to understand.